A Series of Iron Nitrosyl Complexes {Fe-NO}6-9 and a Fleeting {FeNO}10 Intermediate en route to a Metalacyclic Iron Nitrosoalkane

Keilwerth M, Hohenberger J, Heinemann FW, Sutter J, Scheurer A, Fang H, Bill E, Neese F, Ye S, Meyer K (2019)

Publication Type: Journal article

Publication year: 2019

Journal

DOI: 10.1021/jacs.9b08053

Abstract

Iron-Nitrosyls have fascinated chemists for a long time due to the non-innocent nature of the NO ligand that can exist in up to five different oxidation and spin states. Coordination to an open-shell iron center leads to complex electronic structures, which is the reason Enemark and Feltham introduced the {Fe-NO}ⁿ notation.¹ In this work, we succeeded to characterize a series of {Fe-NO}^6-9 complexes, including a reactive {Fe-NO}¹⁰ intermediate. All complexes were synthesized with the tris-N-heterocyclic carbene ligand tris[2-(3-mesityl-imidazol-2-ylidene)ethyl]amine (TIMEN^Mes), which is known to support iron in high and low oxidation states. Reaction of NOBF4 with [(TIMEN^Mes)Fe]²⁺ resulted in formation of the {Fe-NO}⁶ compound [(TIMEN^Mes)Fe(NO)(CH3CN)](BF4)3, (1). Stepwise chemical reduction with Zn, Mg, and Na/Hg leads to the isostructural series of high-spin iron nitrosyl complexes {Fe-NO}^7,8,9 (2 - 4). Reduction of {Fe-NO}⁹ with Cs electride finally yields the highly reduced {Fe-NO}¹⁰ intermediate, key to formation of [Cs[2.2.2.]crypt][(TIMEN^Mes)Fe(NO)], (5) featuring a metalacyclic {Fe-NHC(NO)³⁻} nitrosoalkane unit. All complexes were characterized by single-crystal XRD analyses, temperature and field-dependent SQUID magnetization methods as well as ⁵⁷Fe Mössbauer, IR, UV/vis, multi-nuclear NMR, and dual-mode EPR spectroscopy. Spectroscopy-based DFT analyses provide insight into the electronic structures of all compounds and allowed assignments of oxidation states to iron and NO ligands. An alternative synthesis to the {Fe-NO}⁸ complex was found via oxygenation of the nitride complex [(TIMEN^Mes)Fe(N)](BF4). Surprisingly, the resulting {Fe-NO}⁸ species is electronically and structural similar to the [(TIMEN^Mes)Fe(N)]⁺ precursor. Based on the structural and electronic similarities between this nitrosyl/nitride complex couple, we adopted the strategy, developed by Wieghardt et al.,¹ of extending the Enemark & Feltham nomenclature to nitrido complexes, rendering [(TIMEN^Mes)Fe(N)]⁺ as a {Fe-N}⁸ species.

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Involved external institutions

Max-Planck-Institut für Chemische Energiekonversion (MPI CEC) / Max-Planck-Institute for Chemical Energy Conversion Germany (DE) Max-Planck-Institut für Kohlenforschung (MPI KoFo) / Max Planck Institute for Coal Research Germany (DE)

How to cite

APA:

Keilwerth, M., Hohenberger, J., Heinemann, F.W., Sutter, J., Scheurer, A., Fang, H.,... Meyer, K. (2019). A Series of Iron Nitrosyl Complexes {Fe-NO}6-9 and a Fleeting {FeNO}10 Intermediate en route to a Metalacyclic Iron Nitrosoalkane. Journal of the American Chemical Society. https://doi.org/10.1021/jacs.9b08053

MLA:

Keilwerth, Martin, et al. "A Series of Iron Nitrosyl Complexes {Fe-NO}6-9 and a Fleeting {FeNO}10 Intermediate en route to a Metalacyclic Iron Nitrosoalkane." Journal of the American Chemical Society (2019).

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